Welding is the preferred method of metal joining for most applications where permanent structural configuration is intended. The traditional weld mechanism of melting and initiating the pooling of a portion of each metal has undergone many changes. Since its inception, friction stir welding (FSW) has improved weld efficiency and physical properties of the product joint, among other advantages. Friction stir welding utilizes a rotating tip of appropriate material, which is forced against the butting edges of the weld pieces. The rotating tool produces heat by friction on the workpiece softening the material and mixing it simultaneously. The process does not normally require filler metals and can often be successfully applied without an inert gas cover.
The friction stir welding technique, however, despite its simplicity, has encountered a number of challenges. The relatively high downward/vertical force on the tool required to produce the heating required to initiate the weld virtually necessitates a large machine which renders it impractical to have portable or handheld friction stir welding devices. Recently, there have been developments in friction stir welding technology which have decreased the downward force requirements. These developments are focused on the supplementary heating of workpieces by various methods such as inductance heating, resistance heating, and laser heating. However, the supplementary heating is not typically limited to the immediate region of welding, and may adversely affect a larger region of the workpiece. Consequently, there is a need for a supplemental heating arrangement that localizes the heat transmitted to the workpiece. It is also desired to have a friction stir welding arrangement that reduces the downward/vertical force requirement by as much as 90% to improve the process and to enable the use of handheld/portable tools. Other limitations of conventional friction stir welding include low weld speed and significant tool wear. Accordingly, it is desired to have a friction stir welding apparatus and method that increases the weld speed and reduces the wear on the tool.